Abstract:

Example embodiments are directed to methods of producing desired isotopes
in commercial nuclear reactors and associated apparatuses using
instrumentation tubes conventionally found in nuclear reactor vessels to
expose irradiation targets to neutron flux found in the operating nuclear
reactor. Example embodiments include irradiation targets for producing
radioisotopes in nuclear reactors and instrumentation tubes thereof.
Example embodiments include one or more irradiation targets useable with
example delivery systems that permit delivery into instrumentation tubes.
Example embodiments may be sized, shaped, fabricated, and otherwise
configured to successfully move through example delivery systems and
conventional instrumentation tubes while producing desired isotopes.

Claims:

1. An irradiation target system comprising:at least one irradiation
target,dimensioned to fit within a nuclear reactor instrumentation tube
and to fit within a tubing of a delivery system, andconfigured to join to
the delivery system so as to be movable into the nuclear reactor
instrumentation tube; andconfigured to substantially convert to a
different daughter product when exposed to a neutron flux in an operating
nuclear reactor.

2. The system of claim 1, wherein the at least one irradiation target
includes a first irradiation target positioned at a leading end of a
target portion of the delivery system, the first irradiation target
having an end that tapers to the leading edge.

3. The system of claim 2, wherein the at least one irradiation target
further includes a second irradiation target positioned behind the first
irradiation target from the leading end, the second irradiation target
configured to removably join to a driving portion of the delivery system.

4. The system of claim 3, wherein the at least one irradiation target
further includes at least one third irradiation target positioned between
the first and the second irradiation targets, and wherein the first, the
second, and the third irradiation targets are cylindrical and have a
substantially similar outer diameter.

5. The system of claim 1, wherein the at least one irradiation target is
fabricated of a material substantially converting to a different daughter
product having a half-life of 75 days or less.

6. The system of claim 1, further comprising:a wire passing through and
joining the at least one irradiation target to the target portion,
wherein the at least one irradiation target defines a hole passing
through the irradiation target, the hole having a diameter configured to
secure the at least one irradiation target to the wire.

7. The system of claim 6, wherein the wire is fabricated of a material
substantially converting to a different daughter product having a
half-life of 75 days or less.

8. The system of claim 1, wherein the at least one irradiation target
includes a first irradiation target configured to removably join to a
driving portion of the delivery system.

9. The system of claim 8, wherein the first irradiation target is
configured to join to the driving portion via a threaded end and threaded
hole.

10. An isotope delivery system, comprising:a cable;at least one
irradiation target joined to the cable, the at least one irradiation
target substantially converting to a different daughter product when
exposed to a neutron flux in an operating nuclear reactor;a drive system
configured to move the cable and the at least one irradiation target
retention device into an instrumentation tube of the nuclear reactor;
anda guide configured to guide the cable and the at least one irradiation
target to and from the instrumentation tube of the nuclear reactor.

11. The system of claim 10, wherein the cable includes a driving portion
and a target portion, the target portion being directly joined to the at
least one irradiation target.

12. The system of claim 11, wherein the target portion includes a wire
passing through and joining the at least one irradiation target to the
target portion, wherein the at least one irradiation target defines a
hole passing through the at least one irradiation target, the hole having
a diameter configured to secure the at least one irradiation target to
the wire.

13. The system of claim 11, wherein the at least one irradiation target
includes a first irradiation target positioned at a leading end of the
target portion, the first irradiation target having an end that tapers to
the leading edge.

14. The system of claim 13, wherein the at least one irradiation target
further includes a second irradiation target positioned behind the first
irradiation target from the leading end, the second irradiation target
configured to removably join to the driving portion of the delivery
system.

15. The system of claim 14, wherein the at least one irradiation target
further includes at least one third irradiation target positioned between
the first and the second irradiation targets, and wherein the first, the
second, and the third irradiation targets are cylindrical and have a
substantially similar outer diameter.

16. The method of claim 12, wherein the wire further includes at least one
holding point configured to hold the at least one irradiation target in a
constant position with respect to the wire.

17. A method of producing isotopes in a nuclear reactor with an
irradiation target delivery system, the method comprising:placing at
least one irradiation target into an irradiation target delivery device,
the irradiation target configured to substantially convert to a different
daughter product when exposed to a neutron flux in the operating nuclear
reactor, the irradiation target including a first irradiation target
positioned at a leading end of a target portion of the irradiation target
delivery device, the first irradiation target having an end that tapers
to the leading edge;inserting the irradiation target delivery device into
an instrumentation tube of a nuclear reactor;irradiating the at least one
irradiation target;removing the irradiation target delivery device from
the nuclear reactor; andharvesting the daughter product from the
irradiation target.

18. The method of claim 17, wherein the placing the at least one
irradiation target into the irradiation target delivery device includes
attaching the irradiation target to a wire, pushing the wire through a
first guide and into the instrumentation tube using a drive system.

19. The system of claim 17, wherein the at least one irradiation target
further includes a second irradiation target positioned behind the first
irradiation target from the leading end, the second irradiation target
configured to removably join to a driving portion of the delivery device.

20. The system of claim 19, wherein the at least one irradiation target
further includes at least one third irradiation target positioned between
the first and the second irradiation targets, and wherein the first, the
second, and the third irradiation targets are cylindrical and have a
substantially similar outer diameter.

Description:

BACKGROUND

[0001]1. Field

[0002]Example embodiments generally relate to isotopes and apparatuses and
methods for production thereof in nuclear reactors.

[0003]2. Description of Related Art

[0004]Radioisotopes have a variety of medical and industrial applications
stemming from their ability to emit discreet amounts and types of
ionizing radiation and form useful daughter products. For example,
radioisotopes are useful in cancer-related therapy, medical imaging and
labeling technology, cancer and other disease diagnosis, and medical
sterilization.

[0005]Radioisotopes having half-lives on the order of days are
conventionally produced by bombarding stable parent isotopes in
accelerators or low-power reactors with neutrons on-site at medical or
industrial facilities or at nearby production facilities. These
radioisotopes are quickly transported due to the relatively quick decay
time and the exact amounts of radioisotopes needed in particular
applications. Further, on-site production of radioisotopes generally
requires cumbersome and expensive irradiation and extraction equipment,
which may be cost-, space-, and/or safety-prohibitive at end-use
facilities.

[0006]Because of difficulties with production and the lifespan of
short-term radioisotopes, demand for such radioisotopes may far outweigh
supply, particularly for those radioisotopes having significant medical
and industrial applications in persistent demand areas, such as cancer
treatment.

SUMMARY

[0007]Example embodiments are directed to methods of producing desired
isotopes in commercial nuclear reactors and associated irradiation
targets. Example methods may utilize instrumentation tubes conventionally
found in nuclear reactor vessels to expose irradiation targets to neutron
flux found in the operating nuclear reactor. Desired isotopes may be
produced in the irradiation targets due to the flux. These desired
isotopes may then be relatively quickly and simply harvested by removing
the irradiation targets from the instrumentation tube and reactor
containment, without shutting down the reactor or requiring chemical
extraction processes. The produced isotopes may then be immediately
transported to end-use facilities.

[0008]Example embodiments include irradiation targets for use in nuclear
reactors and instrumentation tubes thereof. Example embodiments may
include one or more irradiation targets useable with example delivery
systems that permit delivery of irradiation targets. Example embodiments
may be sized, shaped, fabricated, and otherwise configured to
successfully move through example delivery systems and conventional
instrumentation tubes.

BRIEF DESCRIPTIONS OF THE DRAWINGS

[0009]Example embodiments will become more apparent by describing, in
detail, the attached drawings, wherein like elements are represented by
like reference numerals, which are given by way of illustration only and
thus do not limit the example embodiments herein.

[0010]FIG. 1 is an illustration of a conventional nuclear reactor having a
plurality of instrumentation tubes.

[0011]FIG. 2 is an illustration of an example embodiment system for
delivering example embodiments into an instrumentation tube of a nuclear
reactor.

[0012]FIG. 3 is a detail view of the example embodiment system of FIG. 2.

[0013]FIG. 4 is a detail view of the example embodiment system of FIG. 3.

[0014]FIG. 5 is an illustration of a conventional nuclear reactor TIP
system.

[0015]FIG. 6 is an illustration of a further example embodiment system for
delivering example embodiments into an instrumentation tube of a nuclear
reactor.

[0016]FIG. 7 is an illustration of several example embodiment irradiation
targets combined with example delivery systems.

[0017]FIG. 8 is an illustration of an example embodiment irradiation
target.

[0018]FIG. 9 is an illustration of another example embodiment irradiation
target.

[0019]FIG. 10 is an illustration of another example embodiment irradiation
target.

[0020]FIG. 11 is an illustration of several example embodiment irradiation
targets combined with an alternate example delivery system.

DETAILED DESCRIPTION

[0021]Detailed illustrative embodiments of example embodiments are
disclosed herein. However, specific structural and functional details
disclosed herein are merely representative for purposes of describing
example embodiments. The example embodiments may, however, be embodied in
many alternate forms and should not be construed as limited to only
example embodiments set forth herein.

[0022]It will be understood that, although the terms first, second, etc.
may be used herein to describe various elements, these elements should
not be limited by these terms. These terms are only used to distinguish
one element from another. For example, a first element could be termed a
second element, and, similarly, a second element could be termed a first
element, without departing from the scope of example embodiments. As used
herein, the term "and/or" includes any and all combinations of one or
more of the associated listed items.

[0023]It will be understood that when an element is referred to as being
"connected," "coupled," "mated," "attached," or "fixed" to another
element, it can be directly connected or coupled to the other element or
intervening elements may be present. In contrast, when an element is
referred to as being "directly connected" or "directly coupled" to
another element, there are no intervening elements present. Other words
used to describe the relationship between elements should be interpreted
in a like fashion (e.g., "between" versus "directly between", "adjacent"
versus "directly adjacent", etc.).

[0024]The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of example
embodiments. As used herein, the singular forms "a", "an" and "the" are
intended to include the plural forms as well, unless the language
explicitly indicates otherwise. It will be further understood that the
terms "comprises", "comprising,", "includes" and/or "including", when
used herein, specify the presence of stated features, integers, steps,
operations, elements, and/or components, but do not preclude the presence
or addition of one or more other features, integers, steps, operations,
elements, components, and/or groups thereof.

[0025]It should also be noted that in some alternative implementations,
the functions/acts noted may occur out of the order noted in the figures.
For example, two figures shown in succession may in fact be executed
substantially and concurrently or may sometimes be executed in the
reverse order, depending upon the functionality/acts involved.

[0026]FIG. 1 is an illustration of a conventional reactor pressure vessel
10 usable with example embodiments and example methods. Reactor pressure
vessel 10 may be used in at least a 100 MWe commercial light water
nuclear reactor conventionally used for electricity generation throughout
the world. Reactor pressure vessel 10 may be positioned within a
containment structure 411 that serves to contain radioactivity in the
case of an accident and prevent access to reactor pressure vessel 10
during operation of the reactor pressure vessel 10. A cavity below the
reactor pressure vessel 10, known as a drywell 20, serves to house
equipment servicing the vessel such as pumps, drains, instrumentation
tubes, and/or control rod drives. As shown in FIG. 1, at least one
instrumentation tube 50 extends vertically into the reactor pressure
vessel 10 and well into or through core 15 containing nuclear fuel and
relatively high amounts of neutron flux during operation of the core 15.
Instrumentation tubes 50 may be generally cylindrical and widen with
height of the reactor pressure vessel 10; however, other instrumentation
tube geometries are commonly encountered in the industry. An
instrumentation tube 50 may have an inner diameter and/or clearance of
about 0.3 inch, for example.

[0027]The instrumentation tubes 50 may terminate below the reactor
pressure vessel 10 in the drywell 20. Conventionally, instrumentation
tubes 50 may permit neutron detectors, and other types of detectors, to
be inserted therein through an opening at a lower end in the drywell 20.
These detectors may extend up through instrumentation tubes 50 to monitor
conditions in the core 15. Examples of conventional monitor types include
wide range detectors (WRNM), source range monitors (SRM), intermediate
range monitors (IRM), and/or Local Power Range Monitors (LPRM).

[0028]Although reactor pressure vessel 10 is illustrated with components
commonly found in a commercial Boiling Water Reactor, example embodiments
and methods may be useable with several different types of reactors
having instrumentation tubes 50 or other access tubes that extend into
the reactor. For example, Pressurized Water Reactors, Heavy-Water
Reactors, Graphite-Moderated Reactors, etc. having a power rating from
below 100 Megawatts-electric to several Gigawatts-electric and having
instrumentation tubes 50 at several different positions from those shown
in FIG. 1 may be useable with example embodiments and methods. As such,
instrumentation tubes 50 useable in example methods may be any protruding
feature at any geometry about the core 15 that allows enclosed access to
the flux of the nuclear core of various types of reactors.

[0029]Applicants have recognized that instrumentation tubes 50 may be
useable to quickly and constantly generate desired isotopes on a
large-scale basis without the need for chemical or isotopic separation
and/or waiting for reactor shutdown of commercial reactors. Example
methods may include inserting irradiation targets into instrumentation
tubes 50 and exposing the irradiation targets to the core 15 while
operating, thereby exposing the irradiation targets to the neutron flux
commonly encountered in the operating core 15. The core flux may convert
a substantial portion of the irradiation targets to a useful
radioisotope, including short-term radioisotopes useable in medical
applications. Irradiation targets may then be withdrawn from the
instrumentation tubes 50, even during ongoing operation of the core 15,
and removed for medical and/or industrial use.

Example Delivery Systems

[0030]Example delivery systems are discussed below in conjunction with
example embodiment irradiation targets useable therewith, which are
described in detail later. It is understood that example embodiment
irradiation targets may be useable with other types of delivery systems
than those described below.

[0031]FIGS. 2-6 are illustrations of related systems for delivering
example embodiment irradiation targets into a nuclear reactor, described
in co-pending application Ser. No. ______, filed on the same date
herewith, entitled "CABLE DRIVEN ISOTOPE DELIVERY SYSTEM," the contents
of which are herein incorporated by reference in their entirety. Example
embodiment irradiation target retaining apparatuses are useable with the
related systems described in FIGS. 2-6; however, it is understood that
other delivery systems may be used with example embodiment irradiation
target retaining apparatuses.

[0032]FIG. 2 illustrates a related cable-driven isotope delivery system
1000 that may use the instrument tubes 50 to deliver example embodiment
irradiation targets into a reactor pressure vessel 10 (FIG. 1). Cable
driven isotope delivery system 1000 may be capable of transferring an
irradiation target from a loading/unloading area 2000, to an
instrumentation tube 50 of reactor pressure vessel 10 and/or from
instrumentation tube 50 of the reactor pressure vessel 10 to the
loading/unloading area 2000. As shown in FIG. 2, cable driven isotope
delivery system 1000 may include a cable 100, tubing 200a, 200b, 200c,
and 200d, a drive mechanism 300, a first guide 400, and/or a second guide
500. The tubing 200a, 200b, 200c, and 200d may be sized and configured to
allow the cable 100 to slide therein. Accordingly, the tubing 200a, 200b,
200c, and 200d may act to guide the cable 100 from one point in the cable
driven isotope delivery system 1000 to another point in the cable driven
isotope delivery system 1000. For example, tubing 200a, 200b, 200c, and
200d may guide cable 100 from a point outside of containment structure
411 (FIG. 1) to a point in instrumentation tube 50 inside containment
structure 411.

[0033]An example cable 100 is illustrated in FIGS. 3 and 4. Example cable
100 may have at least two portions: 1) a relatively long driving portion
110; and 2) a target portion 120. Driving portion 110 of cable 100 may be
fabricated of a material having a low nuclear cross-section, such as
aluminum, silicon, and/or stainless steel. Driving portion 110 of cable
100 may be braided in order to increase the flexibility and/or strength
of cable 100 so that cable 100 may be more easily bendable and capable of
being wrapped around a reel, for example. Although cable 100 may be
easily bendable, cable 100 may additionally be sufficiently stiff in an
axial direction so that cable 100 may be pushed through tubing 200a,
200b, 200c, and/or 200d without buckling.

[0034]As shown in FIG. 4, target portion 120 of example cable 100 may
include a plurality of example embodiment irradiation targets 122. Target
portion 120 may be attached to a first end 114 of the driving portion
110. The length of the target portion 120 may vary depending on a number
of factors, including the irradiation target material, the size and shape
of the example embodiment irradiation targets 122, the amount of
radiation the target is expected to be exposed to, and/or the geometry of
the instrument tubes 50. As an example, the target portion 120 may be
about 12 feet long.

[0035]Referring to FIGS. 3-4, target portion 120 may include a first end
cap 126 at a first end 127 of target portion 120 and a second end cap 128
at a second end 129 of target portion 120. First end cap 126 may be
configured to attach to a first end 114 of driving portion 110. First end
cap 126 and first end 114 of driving portion 110 may form a quick
connect/disconnect connection. For example, first end cap 126 may include
a hollow portion having internal threads 126a. First end 114 of driving
portion 110 may include a connector 113 having external threads that may
be configured to mesh with the internal threads 126a of the first end cap
126. Although the example connection illustrated in FIGS. 3 and 4 is
described as a threaded connection, one skilled in the art would
recognize various other methods of connecting target portion 120 of the
cable 100 to driving portion 110 of cable 100.

[0036]An operator may configure first guide 400 and second guide 500 so
that cable 100 may be advanced to a desired destination. For example,
between loading/unloading area 2000 and instrumentation tube 50.

[0037]After configuring first and second guides 400 and 500, an operator
may operate drive system 300 to advance cable 100 through tubing 200a,
first guide 400, and second tubing 200b to place first end 114 of driving
portion 110 of cable 100 into the loading/unloading area 2000. An
operator may advance cable 100 by controlling a worm gear in drive system
300 that meshes with cable 100. The location of first end 114 of driving
portion 110 of cable 100 may be tracked via markings 116 on cable 100. In
the alternative, position of first end 114 of driving portion 110 of
cable 100 may be known from information collected from a transducer that
may be connected to drive system 300.

[0038]After the cable 100 has been positioned in the loading/unloading
area 2000 example embodiment irradiation targets 122 may then be
connected to cable 100 as described below with reference to example
embodiment irradiation targets. An operator may operate drive system 300
to pull the cable from the loading/unloading area 2000 through tubing
200b and through first guide 400. The operator may then reconfigure first
guide 400 to send cable 100 and example embodiment irradiation targets
122 to reactor pressure vessel 10. After the first guide 400 is
reconfigured, the operator may advance cable 100 through third tubing
200c, second guide 500, fourth tubing 200d, and into a desired
instrumentation tube 50. Location of first end 114 of the driving portion
110 of cable 100 may be tracked via markings 116 on cable 100. In the
alternative, position of first end 114 of driving portion 110 of cable
100 may be known from information collected from a transducer that may be
connected to a worm gear, for example.

[0039]After cable 100 bearing example embodiment irradiation targets 122
has been advanced to the appropriate location within instrumentation tube
50, the operator may stop cable 100 in the instrumentation tube 50. At
this point, irradiation targets 122 may be irradiated for the proper time
in the nuclear reactor. After irradiation, the operator may operate drive
system 300 to pull cable 100 out of instrumentation tube 50, fourth
tubing 200d, second guide 500, third tubing 200c, and/or first guide 400.

[0040]An operator may operate drive system 300 to advance cable 100
through first guide 400, and second tubing 200b to place first end 114 of
driving portion of the cable 100 and example embodiment irradiation
targets 122 into the loading/unloading area 2000. Example irradiation
targets 122 may be removed from cable 100 and stored in a transfer cask
or another desired location. An example transfer cask may be made of
lead, tungsten, and/or depleted uranium in order to adequately shield the
irradiated targets 122. Attachment and detachment of example embodiment
irradiation targets 122 may be facilitated by the use of cameras which
may be placed in the loading/unloading area 2000 to allow an operator to
visually inspect the equipment during operation.

[0041]An alternate delivery system includes use of a conventional
Transverse In-core Probe (TIP) system. A conventional TIP system 3000 is
illustrated in FIG. 5. As shown in FIG. 5, TIP system 3000 may include a
drive system 3300 for driving a cable 3100, and tubing 3200a between
drive system 3300 and a chamber shield 3400, tubing 3200b between chamber
shield 3400 and a valve 3600, tubing 3200c between valve 3600 and a guide
3500, and tubing 3200d between guide 3500 and an instrumentation tube 50.
Cable 3100 may be similar to the cable 100 described with reference to
FIGS. 2-4. Guide 3500 of conventional TIP system 3000 may guide a TIP
sensor to a desired instrumentation tube 50. Chamber shield 3400 may
resemble a barrel filled with lead pellets. The chamber shield 3400 may
store the TIP sensor when not utilized in the reactor pressure vessel 10.
Valves 3600 are a safety feature utilized with the TIP system.

[0042]Because the TIP system includes a tubing system 3200a, 3200b, 3200c,
and 3200d and/or a guide 3500 for guiding a cable 100 into an
instrumentation tube 50, these systems may be used as an example delivery
mechanism for example embodiment irradiation targets 122.

[0043]FIG. 6 illustrates an example delivery system including a modified
TIP system 4000. As shown in FIG. 6, the modified TIP system 4000 is
similar to conventional TIP system 3000 illustrated in FIG. 5, with a
guide 4100 introduced between chamber shield wall 3400 and valves 3600 of
the conventional TIP system 3000. Guide 4100 may serve as an access point
for introducing a cable, for example, cable 100, into modified TIP system
4000. As shown in FIG. 6, drive system 300 (FIG. 2) may be placed in
parallel with drive system 3300 of the modified TIP system 4000. Drive
system 300 may include cable storage reel 320 on which cable 100 may be
wrapped. Tube 200a may extend from the drive system 3300 to guide 400
which may direct cable 100 to a desired location. Rather than having an
exit point that may direct cable 100 to second guide 500 (FIG. 2), first
guide 400 in modified TIP system 4000 may be configured to direct cable
100 to guide 4100 instead. In this way, the first guide 400 may guide
cable 100 into the modified TIP system 4000 tubing via guide 4100.

[0044]Cable 100 should be sized to function with existing tubing in
example delivery systems and permit passage of example embodiment
irradiation targets 122. For example, the inner diameter of tubing 3200a,
3200b, etc. may be approximately 0.3 inches. Accordingly, cable 100 may
be sized so that dimensions transverse to the cable 100 do not exceed 0.3
inches.

Example Embodiment Irradiation Targets

[0045]Example delivery systems being described, example embodiment
irradiation targets useable therewith are now described. It is understood
that example targets devices may be configured/sized/shaped/etc. to
interact with the example delivery systems discussed above, but example
targets may also be used in other delivery systems and methods in order
to be irradiated within a nuclear reactor.

[0046]FIG. 7 is an illustration of example embodiment irradiation targets
122a, 122b, and 122c. As shown in FIG. 7, irradiation targets 122a, b,
and c may be useable with and/or replace some features shown in FIG. 4 in
connection with example delivery devices discussed above. Particularly,
target portion 120 may contain example embodiment irradiation target 122a
in place of second endcap 128 at an end of target portion 120. Target
portion 120 may further contain example embodiment irradiation target
122c in place of first end 127 having endcap 126 with internal threads
126a for connection to driving portion 110 (FIG. 3). Alternatively,
second endcap 128 and/or first endcap 126 may be present and useable with
example embodiment irradiation targets 122a, 122b, and 122c.

[0047]Individual example irradiation targets 122a, 122b, and 122c are
discussed below with reference to FIGS. 8-10. The various example
embodiments, 122a, 122b, 122c, may each be fabricated of or contain one
or more materials that convert to desired daughter products when exposed
to nuclear flux. An irradiation target is a target that is irradiated for
the purpose of generating radioisotopes. Accordingly, sensors, which may
be irradiated by a nuclear reactor and which may generate radioisotopes,
do not fall within the scope of term target as used herein since their
purpose is to detect the state of the reactor rather than to generate
radioisotopes.

[0048]Materials for irradiation targets 122a, 122b, and 122c and amount of
exposure time in instrumentation tube 50 may be selected to determine the
type and concentration of radioisotope produced. That is, because axial
flux levels are known within an operating reactor, and because example
embodiments may permit precise control of axial position of irradiation
targets 122 used in example delivery apparatuses, the type and size of
irradiation targets 122 and exposure time may be used to determine the
resulting radioisotopes and their strength. It is known to one skilled in
the art and from reference to conventional decay and cross-section charts
what types of irradiation targets 122 will produce desired radioisotopes
given exposure to a particular amount of neutron flux. Further,
irradiation targets 122 may be chosen based on their neutron
cross-section, so as to beneficially affect or not interfere with neutron
flux at known axial positions in an operating commercial nuclear reactor
core.

[0049]For example, it is known that Molybdenum-98 may be converted into
Molybdenum-99 having a half-life of approximately 2.7 days when exposed
to a particular amount of neutron flux. In turn, Molybdenum-99 decays to
Technetium-99m having a half-life of approximately 6 hours.
Technetium-99m has several specialized medical uses, including medical
imaging and cancer diagnosis, and a short-term half-life. Using
irradiation targets 122 fabricated from Molybdnenum-98 and exposed to a
neutron flux in an operating reactor based on the size of irradiation
target 122, Molybdenum-99 and/or Technetium-99m may be generated and
harvested in example embodiment assemblies and methods by determining the
mass of the irradiation target containing Mo-98, the axial position of
the target in the operational nuclear core, the axial profile of the
operational nuclear core, and the amount of time of exposure of the
irradiation target. Further, because both Mo-98 and Tc-99m are solids,
example targets may be fabricated entirely of Mo-98 or natural Molybdenum
without need for additional containment, as may be required for liquid or
gaseous targets and daughter products. Other solid target/daughter pairs
may also take advantage of not needing additional containment and
permitting maximum target/daughter mass, including, for example,
Iridium/Platinum.

[0050]FIG. 8 is an illustration of example embodiment irradiation target
122a. Example irradiation target 122a has dimensions that enable it to be
inserted into instrumentation tubes 50 (FIG. 1) used in conventional
nuclear reactors and/or through any tubing used in delivery systems. For
example, irradiation target 122a may have a maximum outer diameter of an
inch or less. Similarly, irradiation target 122a may have a maximum outer
diameter/perimeter substantially equal to that of other irradiation
targets 122b and 122c, so as to provide target portion 120 (FIG. 7) with
a constant maximum outer diameter/perimeter. Example embodiment
irradiation target 122a may be cylindrical; alternatively, example
irradiation target 122a may be a variety of properly-dimensioned shapes,
including spheres, hexahedrons, cones, and/or prismatic shapes.

[0051]Example embodiment irradiation target 122a includes a hole 123a and
a tapering portion 125a. Hole 123a passes through irradiation target 122a
and has a position and diameter that permit wire 124 (FIG. 7) or another
joining mechanism of example retention devices to pass through and hold
irradiation target 122a. Hole 123a may be sized to permit example
embodiment irradiation target 122a to freely slide on captured wire 124
or to frictionally join to captured wire 124 in a static position.

[0052]Tapering portion 125a is positioned at a front end of example
embodiment irradiation target 122a with respect to target portion 120
(FIG. 7). Tapering portion 125a may be smooth and taper at a desired
angle, to or short of hole 123a, so as to provide a wedge-shaped leading
edge of target portion 120. Tapering portion 125a is shaped and
positioned at a leading end of target portion 120 to permit easier
navigation of target portion 120 through tubing in example delivery
systems and instrumentation tubes 50. Tapering portion 125a may reduce or
prevent snagging or pinching in tubing and instrumentation tubes 50 as
target portion 120 is advanced therethrough.

[0053]Example embodiment irradiation target 122a may further include one
or more rounded or chamfered edges 121a. Edges 121a may be rounded,
chamfered, or otherwise made smooth at any point where an edge or
protrusion may snag or rub against exterior tubing or an instrumentation
tube 50, such as in tighter bends of tubing in example delivery devices.
Example embodiment irradiation target 122a may have an overall length
that further facilitates movement through bends of tubing in example
delivery devices and/or instrumentation tubes 50. For example, target
122a may have a total length of approximately 1/2-1 inches in order to
move through bends without becoming caught.

[0054]As shown in FIG. 7, example embodiment irradiation target 122a may
be positioned at a leading end of wire 124. In order to maintain taper
125a at the leading end and facilitate movement of target portion 120
through any tubing and instrumentation tube 50, example embodiment
irradiation target 122a may be joined statically to wire 124 at this
position by, for example, having hole 123a capture and frictionally
prevent movement of irradiation target 122a relative to wire 124.
Alternatively, example embodiment irradiation target 122a may be joined
to other irradiation targets 122b/c and/or to driving portion 110 to
maintain the taper 125a at a leading edge of target portion 120. Still
further, as discussed below, alternate mechanisms for securing example
embodiment irradiation target 122a may be used to maintain taper 125a at
a leading edge of target portion 120.

[0055]FIG. 9 is an illustration of an example embodiment irradiation
target 122b. Example target 122b has dimensions that enable it to be
inserted into instrumentation tubes 50 (FIG. 1) used in conventional
nuclear reactors and/or through any tubing used in delivery systems. For
example, irradiation target 122b may have a maximum outer diameter of 0.3
inches or less. Similarly, irradiation target 122b may have a maximum
outer diameter/perimeter substantially equal to that of other irradiation
targets 122a and 122c, so as to provide target portion 120 (FIG. 7) with
a constant maximum outer diameter/perimeter. Example embodiment
irradiation target 122b may be cylindrical; alternatively, example
irradiation target 122b may be a variety of properly-dimensioned shapes,
including spheres, hexahedrons, cones, and/or prismatic shapes.

[0056]Example embodiment irradiation target 122b may further include one
or more rounded or chamfered edges 121b. Edges 121b may be rounded,
chamfered, or otherwise made smooth at any point where an edge or
protrusion may snag or rub against exterior tubing or an instrumentation
tube 50, such as in tighter bends of tubing in example delivery devices.
Example embodiment irradiation target 122b may have an overall length
that further facilitates movement through bends of tubing in example
delivery devices and/or instrumentation tubes. For example, target 122b
may have a total length of approximately 1/2-1 inches in order to move
through bends without becoming caught.

[0057]Example embodiment irradiation target 122b includes a hole 123b.
Hole 123b passes through irradiation target 122b and has a position and
diameter that permit wire 124 (FIG. 7) or another joining mechanism of
example retention devices to pass through and hold irradiation target
122b. Hole 123b may be sized to permit example embodiment irradiation
target 122b to freely slide on captured wire 124 or to frictionally join
to captured wire 124 in a static position.

[0058]FIG. 10 is an illustration of an example embodiment irradiation
target 122c. Example irradiation target 122e has dimensions that enable
it to be inserted into instrumentation tubes 50 (FIG. 1) used in
conventional nuclear reactors and/or through any tubing used in delivery
systems. For example, irradiation target 122c may have a maximum outer
diameter of a about 0.3 inches or less. Similarly, irradiation target
122c may have a maximum outer diameter/perimeter substantially equal to
that of other irradiation targets 122a and 122b, or first end cap 126, so
as to provide target portion 120 (FIG. 7) with a constant maximum outer
diameter/perimeter. Example embodiment irradiation target 122c may be
cylindrical; alternatively, example irradiation target 122c may be a
variety of properly-dimensioned shapes, including spheres, hexahedrons,
cones, and/or prismatic shapes.

[0059]Example embodiment irradiation target 122c may further include one
or more rounded or chamfered edges 121c. Edges 121c may be rounded,
chamfered, or otherwise made smooth at any point to prevent or reduce the
likelihood that an edge or protrusion may snag or rub against exterior
tubing or an instrumentation tube 50, such as in tighter bends of tubing
in example delivery devices. Example embodiment irradiation target 122c
may have an overall length that further facilitates movement through
bends of tubing in example delivery devices and/or instrumentation tubes
50. For example, target 122c may have a total length of approximately
1/2-1 inches in order to move through bends without becoming caught.

[0060]Example embodiment irradiation target 122c includes a hole 123b.
Hole 123c may pass through target 122b and has a position and diameter
that permit wire 124 (FIG. 7) or another joining mechanism of example
retention devices to pass through and hold irradiation target 122b.
Example embodiment irradiation target 122c may further include internal
threads 126a or other joining mechanism that permits target 122c to be
connected to driving portion 110 (FIG. 3). Further, wire 124 may
originate and be anchored in hole 123c, such that when target 122c is
joined to driving portion 110 via internal threads 126a or other joining
mechanisms, such as adhesives, welding, external fasteners, etc.,
irradiation target 122c may anchor target portion 120 to driving portion
110 of example delivery systems. If wire 124 itself is fabricated from
irradiation target material, then the entire target portion including
example targets 122a, b, and c and wire 124 may be disconnected from
driving portion 110 and harvested once irradiated and converted to
desired daughter products.

[0061]As shown in FIG. 7, one or more example embodiment irradiation
targets 122a/b/c may be strung on wire 124. While example embodiments
have been shown and described in FIG. 7 as having target 122a at a
leading edge, one or more targets 122b in a middle portion, and target
122c joined to a driving portion 110 at a trailing edge in order to
facilitate reduced snag and friction in insertion and removal of
irradiation targets 122 through tubing and instrumentation tubes 50 and
maximize desired daughter product production and harvesting, it is
understood that other orders, combinations, and inclusion of additional
structures among example embodiment irradiation targets 122/a/b/c are all
equally possible.

[0062]Example embodiment irradiation targets 122 a/b/c are shown strung on
wire 124 in order to preserve their position in target portion 120. It is
understood that several other alternate joining mechanisms may be
implemented to secure a position and/or order of example embodiment
targets 122. For example, holes 123a/b/c shown in example embodiment
irradiation targets 122 a/b/c may be internally threaded by internal
threads 126a or have other internal configurations that permit wire 124
to join to and/or be moved through irradiation targets 122 a/b/c. Or for
example, example targets 122a/b/c may be held together by an adhesive
resin configured to maintain its adhesive properties when exposed to
conditions in an instrumentation tube 50 of an operating nuclear reactor.

[0063]As shown in FIG. 11, wire 124 may further include one or more
holding points 124a. Holding points 124a may include washers or knots in
wire 124 expanding the cross section of wire 124 at holding points 124a.
Example embodiment irradiation targets 122a/b/c may further have enlarged
portions of holes 123/a/b/c that permit holding points 124a to be
captured within example embodiment irradiation targets 122 a/b/c so as to
hold irradiation targets 122a/b/c stationary with respect to wire 124.
Holding points 124a may be positioned between irradiation targets
122a/b/c in order to hold irradiation targets 122 a/b/c stationary with
respect to wire 124.

[0064]In this way, one or more irradiation targets 122 may be placed
in/joined to a delivery system, such as the ones illustrated in FIGS.
2-6, and successfully delivered in an instrumentation tube 50 in order to
be irradiated. Example embodiment irradiation targets 122 may permit
several different types of irradiation targets 122 to be placed in
instrumentation tubes 50. Because several example targets 122 may be
placed at precise axial levels within an instrumentation tube 50, it may
be possible to provide a more exact amount/type of irradiation target 122
at a particular axial level within instrumentation tube 50. Because the
axial flux profile may be known in the operating reactor, this may
provide for more precise generation and measurement of useful
radioisotopes in irradiation targets 122 placed within example embodiment
irradiation target retention apparatuses. Several different radioisotopes
may be generated in example embodiments and example methods. Example
embodiments and example methods may have a particular advantage in that
they permit generation and harvesting of short-term radioisotopes in a
relatively fast timescale compared to the half-lives of the produced
radioisotopes, without shutting down a commercial reactor, a potentially
costly process, and without hazardous and lengthy isotopic and/or
chemical extraction processes. Although short-term radioisotopes having
diagnostic and/or therapeutic applications are producible with example
apparatuses and methods, radioisotopes having industrial applications
and/or long-lived half-lives may also be generated.

[0065]Example embodiments thus being described, it will be appreciated by
one skilled in the art that example embodiments may be varied through
routine experimentation and without further inventive activity.
Variations are not to be regarded as departure from the spirit and scope
of the exemplary embodiments, and all such modifications as would be
obvious to one skilled in the art are intended to be included within the
scope of the following claims.